php image protection

i have asked this question before on experts exchange but didn't get right answer.

here is the problem.

i am showing an image on page but i don't want people to download it. what i have done right now is disabled right click so that naive users cannot download directly, but i know disabling right click is like no protection at all. so i want a system where images are produced by php file like say i call

<a href="imahe.php?src=image.jpg">thumbnail</a>

and image is produced but if some one accesses the script directly then he should get blank screen. previously i used sessions. when file was being accessed from my gallery page session['show'] is set to1 but when it is accessed directly session['show] is set to 0 and it was working well for me. but i found this plugin for firefox .. coolpreviews which gave user ablity to show download image no matter what.

don't know if i am being very clear here or not. but i would like if some one could help me with it.
thanks in advance

It's extremely difficult to prevent people that really want a copy of your image... consider a screenshot tool, no script will block it.
Check out this link for some decent ideas though: http://www.webresourcesdepot.com/10-ways-to-protect-images-from-being-stolen/

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Many web sites contain image galleries; a common design for these galleries includes a page with a collection of thumbnail images. You can click on each of the thumbnail images to see the larger version of the image. This is easily i…